Mould for encapsulating parts of elements into a plastic material

ABSTRACT

The invention relates to a mould for encapsulating parts of elements into a plastic material to manufacture electric components. The mould comprises a number of steel blocks or rods with accurately finished surfaces for clamping them completely tight together in a holder, whereby recesses in said blocks or rods are forming the mould cavity or mould cavities and the sprues. A layer of high hardness, such as a nitride layer, is deposited by means of vapor deposition in vacuum at a high temperature onto at least those surfaces of said blocks or rods determining the mould cavity or mould cavities and the sprues. Furthermore the blocks or rods are concerning their dimensions and/or flexibility and/or structure and/or finishing of the surfaces turned away from the mould cavity embodied such that deformations in the position in which said blocks or rods are clamped into said holder, caused by the depositioning of said layer, are eliminated.

The invention relates to a mould for encapsulating parts of elementsinto a plastic material to manufacture electronic components, whichmould comprises a number of steel blocks or rods, with accuratelyfinished surfaces for clamping them completely tight together in aholder, in which clamped position recesses in said blocks or rodsdetermine the mould cavity or mould cavities and the sprues, which mouldhas provisions for releasing the injected plastic material from themould after hardening of said plastic and after opening of said mould.

Such moulds are known from the prior art and these prior art mouldscomprise a number of rods which accurately fitting can be clamped into aholder and which have a large number of mould cavities. Said rods have alength of approximately 200 mm, a height of approximately 15 mm and awidth which is varying between 2 mm and for instance 60 mm, said widthis dependent of the normalized dimensions of electronic components. Thedivision up into rods or blocks is necessary because otherwise noaccurate finishing of the mould cavities is possible, which mouldcavities are lapped as smooth as possible. The blocks are veryaccurately finished to obtain a completely tight closure of the blocksagainst each other. The fluidized plastic material is not allowed topenetrate between the blocks. Said prior art moulds are very expensiveand it is difficult to release the plastic after hardening. The plasticis a thermo hardening plastic which in the moulten condition is injectedand hardens inside the mould. Said prior art moulds have very fine andvery accurately finished passages for moving release pins there through.It will be clear that the plastic material is not allowed to penetrateinto said passages.

There are already a number of different proposals to eliminate the abovemenntioned disadvantages.

In the Dutch Patent Application No. 77,04937 the electronic elements areenclosed into prefabricated thermoplastic cups, after which the spacebetween the element and the cup is filled with a thermo hardeningplastic. After hardening the cup forms an integral part of the obtainedcomponent. In this method it is not necessary to use a complicatedmould. It is however disadvantageous that additional steps areintroduced in the manufacturing of electronic components: the cups haveto be fabricated and brought around the electronic element. Furthermoreit is very unlikely that such a construction will be effective withinthe scope of the advancing miniaturisation. With very small elements thehollow space between the case and the component will be so small thatthe injection of the thermoharding plastic in the cup and the adherenceof the cup to the element will become problematical. With increasingdimensional reduction of the component it is not possible to reduce thewall thickness of said cup in the same amount. Furthermore removing theair present inside said cups will become problematrical.

In the European Pat. No. 0 007 762 a mould is described comprising twoflat lower and upper mould sections and a central section with openings,comprising the mould cavities. In the upper mould section only channelsfor injecting the plastic and a few release pins are necessary. The verycomplicated functioning of this mould, caused by a large number ofsections which have to be brought together, is considered asdisadvantageous. Also still a number of release pins are used andfurthermore the plastic can only be injected in the illustrated mouldfrom the upper side. That means that automation is only possible on avery restricted scale.

An object of the invention is now the provide a mould for encapsulatingparts of elements into a thermohardening plastic, which mould is veryeasy to manufacture, and whereby releasing the encapsulating elements isvery easy, so that automation is possible.

In agreement with the invention the above mentioned provisions are nowexclusively embodied as a layer of high hardness, such as a nitridelayer, deposited by means of vapour deposition in vacuum at a hightemperature onto at least those surfaces of the blocks or rodsdetermining the mould cavity or mould cavities and the sprues, whichblocks or rods are furthermore concerning their dimensions and/orflexibility and/or structure and/or finishing of the surfaces at theback side of the mould cavity embodied such, that deformations in theposition in which said blocks or rods are clamped into said holder,caused by depositing said layer, are eliminated.

The advantages of this mould according to the invention are:

a. the encapsulated elements can be released very easily

b. no release pins are necessary, so that the costs of the mould can besignificantly reduced.

c. because the plastic does not anymore adhere to the mould said mouldbecomes not polluted and therefore does not have to be cleaned whichopens the way to automation.

It is remarked that it is known to provide moulds, used withthermoplastic materials, with a hard nitride layer deposited by means ofvapour deposition to extend the live of said mould. These moulds arehowever not suitable for encapsulating electronic parts. The dimensionsof electronic components are very small and the requirements to theaccuracy of the moulds are significantly higher than in the case ofusual moulds for injection mould of thermoplastic or thermohardeningmaterial.

By making the mould of a sintered material, for instance sintered steelwarpening during the depositioning of the nitride layer is avoidedresulting into a mould with very favourable mechanical qualities.

It is also possible to embody the mould such that the blocks or rodsadjoining in longitudinal direction have such a small length thatdimensional deviations of surfaces determining the mould cavity arewithin acceptable tolerance limits. The length of said blocks is in thatcase so small that eventual warpening because of the small length ishardly of any interest.

The mould may have blocks or rods of which the dimensions in length,width and/or height direction are not or only slightly different, sothat deformations of the shape caused by the high temperatures duringthe vapour depositioning of the nitride layer are in all directionsapproximatrely equal so that warpening is avoided.

Furthermore the rods of the mould can be made flexible, so that warpenedrods will be become straightened in the mould clamping device. Apossibility therefore is providing the blocks or rods with transverseslots at that side turned away from the surfaces determining the mouldcavity.

In combination with one or more of the above mentioned measurements orseparate therefrom warpening of the mould during the depositioning ofthe nitride layer can be restricted by the way in which the mouldmaterial is taken out of a piece of rolled steel. It appears the thewarpening is minimized in case the direction in which the steel isrolled is perpendicular to the largest dimension of said blocks or rods,for instance perpendicular to the longitudinal direction.

It is known to configurate a mould with one or more series of mouldcavities. The adjoining parts comprise in that case each a number ofidentical sections of the mould cavities and the sprues. Where it ispossible often the rows of connecting pins of integrated circuits arealigned to simplify the processing. If however the integrated circuitsare mutually positioned such that the connecting pins are interlocking,then the mould cavities have to be dislocated turn and turn. That savesspace so that a larger number of elements can be treated in one mould,however the mould itself becomes more expensive.

Within the scope of the invention it is now possible that each mouldcavity or each pair of mould cavities is positioned into a separateblock with the centerline at a distance for but parallel to thecenterline of the mould.

In that case one still has the advantage that the blocks are alignedduring machining and finishing. Thereafter the separate blocks are turnin turn rotated over 180° in the plane of the mould cavity so that themould cavities become mutually dislocated.

That is possible because within the scope of the invention blocks areused having a very small length.

According to a further embodiment the layer provided by vapourdepositioning in vacuum is a titanium nitride layer.

The invention will now be explained in more detail with reference to theaccompanying drawings in which:

FIG. 1 illustrates a part of the mould according to the invention in aperspective view.

FIG. 2 illustrates a flexible mould block according to the invention.

FIG. 3 ilustrates a strip of material to be treatened, having alignedconnecting pins.

FIG. 4 illustrates a strip of material to be treated with mutuallyinterlocking connecting pins.

FIG. 5 illustrates the positioning of the mould blocks according to FIG.2 into a mould for treating a strip as is illustrated in FIG. 4.

In FIG. 1 the block 1 of a mould is illustrated comprising the sprue 2.Said sprue is in agreement with the copending Dutch Patent ApplicationNo. 82,03253 positioned sidelong the mould, however, the sprue can alsobe positioned at the upper or lower side of the mould. The strip ofmaterial with the elements illustrated in FIG. 3 or 4 is placed onto theupper surface 14 of the block 1, whereby the connecting pins of theelements are fitting between the cams 9. It is important that theconnecting pins are maintained free of plastic material so thatafterwards it is possible to bend the connecting pins of the readyelectronic component. Thereafter the (not illustrated) upper block isplaced onto said block 1 such that the davel pins 8 of block 1 arefitting into said counterpart. In this upper counterpart only recessesfor the uppersection of the electronic elements to be encapsulated areprovided. Thereafter the thermo hardening fluid is injected through thesprue 2. After (at least partly) hardening the upper mould blocks areelevated and the treated element or strip of elements can be removed.Because of the presence of the hard titanium nitride layer in the mouldcavity and in the sprue the plastic material will release without theuse of releasing pins. Because furthermore the adherence of the plasticmaterial is very poor pollution of the mould is prevented so that it isnot necessary to clean the mould between the succeeding productionsteps. The result thereof is that a far reaching automation is possible.As appears from FIG. 1 the illustrated mould block has an approximatelysquare upper surface with a recess 4. The height is smaller than thewidth respectively the length. Provisions are taken to prevent warpeningof the mould when the hard nitride layer is deposited by vapourdeposition in vacuum because thereafter the mould cannot be lappedanymore.

Because of the small length, which is for instance 1/10 of the length ofknown mould blocks, the deformation as a result of the high temperatureduring the allround depositioning of the hard layer does practically nothave any influence.

In FIG. 2 a further embodiment of a mould block according to theinvention is illustrated. The significant difference with the mouldblock illustrated in FIG. 1 is that this mould block has an elongatedshape. This mould block has recesses 7 resulting into a flexible mouldblock. By clamping this mould blocks with their free "legs" 18, 19, 20onto a flat base surface deformation will be eliminated.

In FIG. 3 a strip of material 10, in general copper with chips 11 andaligned connecting pins 6 is illustrated. In the strip of materialillustrated in FIG. 4 the connecting pins 6 are turn and turndislocated. That results into a shorter configuration so that in eachmould a larger number of elements can be treatened.

Finally in FIG. 5 the positioning of the separate mould blocks 13 into amould destined for treating a strip of material illustrated in FIG. 4 isshown. The separate mould blocks are comparable with the mould block ofFIG. 2. By using mould blocks having only one mould cavity or twoadjacent mould cavities, which blocks have to be positioned adjacent toeach other in longitudinal direction into the mould, the machining andfinishing thereof in longitudinal direction becomes very simple.

After machining and finishing the blocks are turn and turn rotatedresulting into the configuration which is schematically indicated inFIG. 5.

In each block 13 the mould cavity 21 has a larger distance to the side22 than the distance from the cavity 23 to the side 24, which differencein distance is determining for the dislocated configuration andtherefore is equal to half the distance 12 between the connecting pins 6of FIG. 4.

I claim:
 1. A mould assembly for encapsulating a plurality of electroniccomponents in an encapsulation material, which mould assembly comprisesa holder and a plurality of elements made from steel and havingaccurately finished surfaces such that said plurality of elements fittogether within the holder and can be clamped tightly in the holder;wherein each element has a mould cavity for said encapsulating, andsprues for supplying said encapsulation material to said mould cavity;wherein said elements of the mould each have at least on that surfacewithin which the cavity is formed, and including the surface of saidcavity, a hardened layer deposited by means of vapour in a vacuum athigh temperature; and wherein said elements have a structure and finishsuch that deformation of each element resulting from the depositionoperation is effectively eliminated when said elements are clamped insaid holder.
 2. A mould according to claim 1, wherein said hardenedlayer is the only means for releasing said plastic encapsulatedcomponents from said mould.
 3. A mould according to claim 2, whereinsaid mould incorporates no release pins.
 4. A mould according to claim1, wherein said hardened layer is a nitride layer.
 5. A mould accordingto claim 4, wherein said nitride layer is a titanium nitride layer.
 6. Amould according to claim 4, wherein said elements are made of sinteredmaterial.
 7. A mould according to claim 1, wherein said elements are aplurality of blocks.
 8. A mould according to claim 7, wherein aplurality of said blocks are adjoined in a longitudinal direction insaid holder.
 9. A mould according to claim 8, wherein the length of saidblocks in said longitudinal direction is sufficiently small so thatdimensional deviations of the surfaces determining said mould cavitiesdo not develop deformations in said blocks when clamped in said holder.10. A mould according to claim 9, wherein said blocks are dimensioned sothat the length, width and height of said blocks are approximately thesame.
 11. A mould according to claim 10, wherein said blocks areflexible.
 12. A mould according to claim 9, wherein said blocks areelongated, and wherein said elongated dimension is generally transverseto said longitudinal direction.
 13. A mould according to claim 12,wherein said blocks are flexible.
 14. A mould according to claim 13,wherein said blocks have transverse slots formed in a side of saidblocks away from the surfaces determining said mould cavities.
 15. Amould according to claim 12, wherein said steel is rolled in a directionperpendicular to said elongated dimension of said blocks.
 16. A mouldaccording to claim 1, wherein said mould comprises a plurality of blocksclamped in said holder so that the mould cavities of adjacent blocks arepositioned generally along a centerline in said mould.
 17. A mouldaccording to claim 16, wherein said components are integrated circuitsincluding a plurality of connecting pins joined end to end in a series.18. A mould according to claim 16, wherein said mould cavities areoffset and positioned at a distance from but parallel to saidcenterline.
 19. A mould according to claim 18, wherein said componentsare integrated circuits including a plurality of connecting pins andjoined end to end in a series, and wherein the connecting pins ofadjacent integrated circuits in said series are interlocking.
 20. Amould according to claim 19, wherein said offset distance substantiallyequals one half of the distance between adjacent connecting pins of oneof said integrated circuits.
 21. A mould according to claim 18, whereinalternating mould cavities are offset from said centerline in oppositedirections.
 22. A mould according to claim 21, wherein each of saidblocks are manufactured with said mould cavities offset in said blocksin the same direction, and wherein adjacent blocks in said series arerespectively rotated 180° when clamped in said holder.
 23. A mouldaccording to claim 1, wherein said elements are structured and finishedsuch that warp of the elements resulting from the deposition operationis effectively eliminated.